A compressor is generally used in an air conditioner, a refrigerator and so on for refrigerant compression. A typical example of such a compressor is shown in FIG. 1.
Referring to FIG. 1, a stator 2 and a rotor 3 are installed in a housing 1. In the rotor 3, provided is a rotary axis 4, which is rotatably supported by upper and lower flanges 5 and 6. Also, an eccentric roller 7 is rotatably mounted in a cylinder 8 between the upper and lower flanges 5 and 6 at a lower end of the rotary axis 4.
In the compressor having such configurations, when the rotor 3 turns to rotate the rotary axis 4, the eccentric roller 7 under the rotor 3 also rotates in the cylinder 8 so as to compress refrigerant gas, which is inhaled through an inflow pipe 9 therein, at high temperature and high pressure and discharge the same out of the cylinder 8. The refrigerant gas compressed as above is then exhausted through a discharge pipe 10, which is at an upper portion of the housing 1, and then circulates in a refrigeration cycle.
The upper and lower flanges, called as main bearing and sub-bearing respectively, of the conventional compressor, which support the rotary axis, are usually made using powder metallurgy in consideration of precision, performance, price competitiveness, etc. However, because the rotary axis, which is the core of driving the compressor, is installed to pass through a hollow portion of the flange, the flange may be deformed on the occasion that the rotary axis deforms due to the driving force. This deformation of the rotary axis may not only deform the flange but also cause melted-bond or abrasion of the flange with the eccentric roller or breakdown of an oil film, which may result in deteriorating performance of the compressor and generating noise.
Recently, to prevent deformation of the flange due to the rotary axis deformation as above, there has been proposed a compressor, which has a relief groove 5b around a hollow portion 5a of the flange 5, as shown in FIG. 2. The relief groove 5b is generally either formed by executing a mechanical cutting process after making the flange or made using a mold in a shaping process of the powder metallurgy method. However, the former mechanical cutting process should be separately performed after molding the flange, so inevitably causing a substantial cost hike. The later using the mold requires, separately, making the mold in a shape corresponding to the relief groove. Moreover, a molding portion corresponding to the relief groove is so weak to be easily broken down or damaged, which causes lower productivity. Furthermore, since the flange manufactured according to a conventional manner has weak portions around the relief groove, sealing of the flange is not ensured, which is one of basic requirements of the flange.